U.S. patent number 9,198,082 [Application Number 13/755,347] was granted by the patent office on 2015-11-24 for method and system for autonomous channel coordination for a wireless distribution system.
This patent grant is currently assigned to InterDigital Technology Corporation. The grantee listed for this patent is INTERDIGITAL TECHNOLOGY CORPORATION. Invention is credited to Paul Marinier, Vincent Roy, Marian Rudolf, Maged M. Zaki.
United States Patent |
9,198,082 |
Marinier , et al. |
November 24, 2015 |
Method and system for autonomous channel coordination for a
wireless distribution system
Abstract
A method and system for autonomous channel coordination for a
wireless distribution system (WDS) are disclosed. A wireless
communication system includes a plurality of access points (APs)
and the APs communicate each other via a WDS. A coordinated channel
group (CCG) of a plurality of member APs is established. The member
APs of the CCG camp on a WDS channel used for the WDS among the
member APs of the CCG. One AP among the member APs of the CCG is
designated as a master AP. The master AP coordinates with other
member APs of the CCG for selecting and configuring the WDS channel
for the CCG and addition and deletion of member APs. By allowing
APs to define a CCG, changes of the WDS channel are performed
autonomously while maintaining connectivity.
Inventors: |
Marinier; Paul (Brossard,
CA), Rudolf; Marian (Montreal, CA), Zaki;
Maged M. (San Diego, CA), Roy; Vincent (Longueuil,
CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
INTERDIGITAL TECHNOLOGY CORPORATION |
Wilmington |
DE |
US |
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Assignee: |
InterDigital Technology
Corporation (Wilmington, DE)
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Family
ID: |
37912474 |
Appl.
No.: |
13/755,347 |
Filed: |
January 31, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20130142068 A1 |
Jun 6, 2013 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13485429 |
May 31, 2012 |
8411636 |
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11554786 |
Jun 5, 2012 |
8194599 |
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60732779 |
Nov 2, 2005 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
84/20 (20130101); H04W 28/18 (20130101); H04W
72/005 (20130101); H04W 48/10 (20130101); H04W
16/02 (20130101); H04W 92/02 (20130101); H04W
16/10 (20130101); H04W 92/20 (20130101) |
Current International
Class: |
H04M
1/66 (20060101); H04W 84/20 (20090101); H04W
28/18 (20090101); H04W 92/02 (20090101); H04W
48/10 (20090101); H04W 16/10 (20090101); H04W
16/02 (20090101); H04W 92/20 (20090101) |
Field of
Search: |
;455/453,450,452.1,422.1,41.2 ;370/329,338,315,310,406,238,389
;709/228 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1311087 |
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May 2003 |
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EP |
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1 727 312 |
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Nov 2006 |
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EP |
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99115640 |
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Jul 2001 |
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RU |
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1436619 |
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May 2014 |
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TW |
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98/19400 |
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May 1998 |
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WO |
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2005/086420 |
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Sep 2005 |
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WO |
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Other References
Agre et al., Secure NOmadic Wireless Mesh (SnowMesh) 802.11 TGs ESS
Mesh Networking Proposal, IEEE 802.11-05/596r1, Retrieved from
http://www.flacp.fujitsulabs.com/snowmesh.pdf on Aug. 9, 2007, (May
15, 2005). cited by applicant .
Cervello et al., Dynamic Channel Selection (DCS) Scheme For 802.11,
IEEE 802.11-00/195, (Jul. 12, 2000). cited by applicant .
IEEE LAN/ MAN Standards Committee, ANSI/IEEE Std. 802.11, 1999
Edition (R2003), Information Technology--Telecommunications And
Information Exchange Between Systems--Local And Metropolitan Area
Networks--Specific Requirements, Part 11: Wireless LAN Medium
Access Control (MAC) and Physical Layer (PHY) Specifications,
(Reaffirmed Jun. 12, 2003). cited by applicant .
IEEE, IEEE P802.11v.TM. /D0.05, Draft Amendment To Standard For
Information Technology--Telecommunications And Information Exchange
Between Systems--LAN/MAN Specific Requirements--Part 11: Wireless
Medium Access Control (MAC) and Physical Layer (PHY)
Specifications, Amendment v: Wireless Network Management, (Sep.
2006). cited by applicant .
Sheu et al., IEEE P802.11 Wireless LANS: 802.11 TGs MAC Enhancement
Proposal, IEEE 802.11-05/0575r3 (Sep. 2005). cited by
applicant.
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Primary Examiner: Patel; Mahendra
Attorney, Agent or Firm: Condo Roccia Koptiw LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. patent application Ser.
No. 13/485,429 filed May 31, 2012, which is a continuation of U.S.
patent application Ser. No. 11/554,786 filed on Oct. 31, 2006,
which issued as U.S. Pat. No. 8,194,599 on Jun. 5, 2012, which
claims the benefit of U.S. Provisional Application No. 60/732,779
filed Nov. 2, 2005, which is incorporated by reference as if fully
set forth.
Claims
What is claimed is:
1. A method for establishing a coordinated group of access points
(APs), the method comprising: an AP sending a first beacon
periodically, wherein the AP becomes a master of a coordinated
group of APs by sending the first beacon including a first field
indicating an identity of the coordinated group and a second field
indicating that the AP sending the first beacon is the master of
the coordinated group; and the AP receiving a second beacon
transmitted by a member AP of the coordinated group, wherein the
second beacon includes a third field indicating the identity of the
coordinated group that is included in the first beacon.
2. The method of claim 1 wherein the AP controls operational
settings in the coordinated group of APs.
3. The method of claim 1 wherein the AP provides connectivity and
synchronization for the member AP.
4. The method of claim 1 wherein the second beacon includes a
fourth field indicating that a sender of the second beacon is the
member AP and not the master of the coordinated group.
5. The method of claim 1 wherein the second beacon includes
capability information of the member AP.
6. The method of claim 5 wherein the capability information
includes at least one of a list of frequency channels that the
member AP supports, information as to whether the member AP is
capable of reporting channel utilization and interference
measurement, or information related to a basic service set (BSS)
served by the member AP.
7. The method of claim 1 further comprising: the AP receiving
measurements from the member AP.
8. The method of claim 7 wherein the measurements include at least
one of interference level measured on each channel, channel
utilization of each channel, number of stations (STAs) detected on
each channel, or identities of STAs associated to the member
AP.
9. The method of claim 7 wherein the measurements include
measurements reported by STAs associated to the member AP.
10. An access point (AP) configured to establish a coordinated
group of APs, the AP comprising: a controller configured to send a
first beacon periodically, wherein the AP becomes a master of a
coordinated group of APs by sending the first beacon including a
first field indicating an identity of the coordinated group and a
second field indicating that the AP sending the first beacon is the
master of the coordinated group; and the controller configured to
receive a second beacon transmitted by a member AP of the
coordinated group, wherein the second beacon includes a third field
indicating the identity of the coordinated group that is included
in the first beacon.
11. The AP of claim 10 wherein the controller is configured to
control operational settings in the coordinated group of APs.
12. The AP of claim 10 wherein the AP provides connectivity and
synchronization for the member AP.
13. The AP of claim 10 wherein the second beacon includes a fourth
field indicating that a sender of the second beacon is the member
AP and not the master of the coordinated group.
14. The AP of claim 10 wherein the second beacon includes
capability information of the member AP.
15. The AP of claim 14 wherein the capability information includes
at least one of a list of frequency channels that the member AP
supports, information as to whether the member AP is capable of
reporting channel utilization and interference measurement, or
information related to a basic service set (BSS) served by the
member AP.
16. The AP of claim 10 wherein the controller is configured to
receive measurements from the member AP.
17. The AP of claim 16 wherein the measurements include at least
one of interference level measured on each channel, channel
utilization of each channel, number of stations (STAs) detected on
each channel, or identities of STAs associated to the member
AP.
18. The AP of claim 16 wherein the measurements include
measurements reported by STAs associated to the member AP.
Description
FIELD OF INVENTION
The present invention is related to wireless communication systems.
More particularly, the present invention is related to a method and
system for autonomous channel coordination for a wireless
distribution system (WDS).
BACKGROUND
In a WLAN system such as 802.11, stations (STAs) within a basic
service set (BSS) share the same frequency channel to communicate
with each other. In an infrastructure-mode BSS, an access point
(AP) relays traffic to and from a distribution system (DS). Many
BSSs can be connected to the DS through their APs. Communication
between APs and other nodes within a DS can be supported by any
medium access control (MAC) scheme, such as IEEE 802.3 in the case
where a wired infrastructure exists. If a wired infrastructure does
not exist, communication between APs can also take place
wirelessly. A set of APs communicating wirelessly constitutes a
WDS.
For successful communication between two APs in a WDS, the sending
AP must transmit a packet on the channel used by the receiving AP.
Generally, APs may choose the channel, (i.e., WDS channel), from a
plurality of available channels to communicate with other APs.
Typically, the WDS channel is same as the BSS channel used by an AP
to transmit and receive packets to and from STAs in its own BSS. In
the prior art, the WDS channel is configured manually by a system
administrator and the APs are not capable of dynamically changing
the WDS channel autonomously.
However, the manual configuration and setup is cumbersome,
error-prone and costly. In addition, the most suitable WDS channel
for communication within the WDS changes dynamically on a
short-term basis due to changes in interference and traffic
conditions. It is not realistic to manually keep track of these
changes and change the WDS channel.
Therefore, it would be desirable to provide a method and system for
autonomously configuring the WDS channel while maintaining
connectivity within the WDS.
SUMMARY
The present invention is related to a method and system for
autonomous channel coordination for a WDS. A wireless communication
system includes a plurality of APs and the APs communicate each
other via a WDS. A coordinated channel group (CCG) comprising a
plurality of member APs is established. The member APs of the CCG
camp on a WDS channel used for the WDS among the member APs of the
CCG. One AP among the member APs of the CCG is designated as a
master AP. The master AP coordinates with other member APs of the
CCG for selecting and configuring the WDS channel for the CCG and
addition and deletion of member APs. By allowing APs to define a
CCG, changes of the WDS channel are performed autonomously while
maintaining connectivity within the WDS.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an exemplary wireless communication system with a WDS
in which the present invention is implemented.
FIG. 2 is a signaling diagram of a process for exchanging messages
for joining a CCG between an AP and a master AP in accordance with
the present invention.
FIG. 3 is a signaling diagram of a process for exchanging messages
for leaving a CCG between an AP and a master AP in accordance with
the present invention.
FIG. 4 is a signaling diagram of a process for exchanging messages
for channel change between an AP and a master AP in accordance with
the present invention.
FIG. 5 is a signaling diagram of a process for exchanging messages
for reselecting a master AP between an AP and a master AP in
accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereafter, the terminology "STA" includes but is not limited to a
wireless transmit/receive unit (WTRU), a user equipment (UE), a
fixed or mobile subscriber unit, a pager, or any other type of
device capable of operating in a wireless environment. When
referred to hereafter, the terminology "AP" includes but is not
limited to a base station, a Node-B, a site controller or any other
type of interfacing device in a wireless environment.
The features of the present invention may be incorporated into an
integrated circuit (IC) or be configured in a circuit comprising a
multitude of interconnecting components.
FIG. 1 shows an exemplary wireless communication system 100 with a
WDS in which the present invention is implemented. The system 100
includes a plurality of APs 102a-102d. Each of the APs 102a-102d
serves its own BSS 106a-106d, (or independent BSS, hereinafter
collectively "BSS"), respectively. The APs 102a-102d are capable of
sending WDS traffic via a WDS established among the APs 102a-102d.
The WDS traffic may be a packet sent from an AP in one BSS to an AP
in another BSS, or a packet sent from a STA in one BSS to a STA in
another BSS. The APs 102a-102d camp on a WDS channel used for the
WDS traffic so that the APs 102a-102d transmit and receive WDS
traffic on the common WDS channel.
The APs 102a-102d may be equipped with a single radio transceiver,
(i.e., the APs need to share their radio transceiver for both their
own BSS traffic and WDS traffic), or more than one radio
transceiver. The WDS channel that the APs 102a-102d camp on may be
different from the channel used to serve STAs 104a-104d in their
own BSS 106a-106d, (i.e., BSS channel). If the WDS channel is
different from the BSS channel, the AP 102a-102d should be able to
simultaneously receive packets on more than one channel. An AP
102a-102d may be able to camp on more than one WDS channel.
In accordance with the present invention, at least one coordinated
channel group (CCG) comprising a plurality of member APs is
established. For example, in FIG. 1, APs 102a-102c belong to a CCG
108 and a common WDS channel is used for the WDS traffic in the CCG
108. In accordance with the present invention, the WDS channel may
be dynamically changed and configured by coordinating APs 102a-102c
in the CCG 108. By being part of the CCG 108, the APs 102a-102c are
ensured of maintaining connectivity with all other APs 102a-102c
that belong to the CCG 108. Furthermore, the APs 102a-102c may be
ensured of maintain connectivity with APs, (such as AP 102d),
belonging to other CCGs if certain rules are followed in the
assignment of CCGs to APs.
Certain APs may or may not have the capability of transmitting
packets to other APs of the WDS on a frequency channel different
from the one they are camping on. In order to maintain connectivity
with other APs of the WDS, an AP not equipped with this capability
should never create a new CCG unless it is the only AP being active
in the environment. Similarly, the selection of the master of a CCG
could be performed manually through operation, administration and
maintenance (OAM). If this approach is selected, the APs not
selected as CCG master in the OAM configuration should be precluded
from attempting to create a new CCG (in which case they would
automatically become master of the newly created CCG). An AP may be
part of as many CCGs as the number of channels on which it is
capable of camping.
One of the APs 102a-102c of the CCG 108 is designated as a master
AP, (e.g., AP 102a). The master AP may be designated autonomously
or by manually through OAM. The master AP 102a accepts or rejects
requests from other non-member APs, (such as AP 102d), to be a part
of the CCG 108, collects relevant information from the member APs
102b, 102c within the CCG 108 to make a WDS channel change
decision, (including requests from member APs 102b, 102c to perform
a channel change), executes a WDS channel change, and executes
changes of other parameters, (such as transmission power, a clear
channel assessment (CCA) mode (or the like), admission control
parameters or other relevant operational settings), that may affect
the performance of the system. CCA is a function that determines if
the medium is busy in IEEE 802.11. The CCA mode (or something
similar in other types of systems) defines how this determination
is made exactly, (e.g., compare to a threshold or not, nature of
the signal, or the like).
An AP 102a-102c that is part of the CCG 108 for a given WDS channel
periodically broadcasts, multicasts or unicasts a CCG indicator
(CCGI) on the WDS channel. The CCGI is a unique identifier, (e.g.,
label, code, alpha-numeric designation, number, or the like). The
CCGI may be included in an existing frame, (such as a beacon frame
or a probe response frame), or a stand-alone (management) frame
dedicated to the CCG functionality. The master AP 102a sets a
master indicator, (e.g., a flag, a bit field or an identification
string), associated to the CCGI to indicate that the AP 102a is the
master of the CCG 108. Only the master AP 102a sets the master
indicator.
FIG. 2 is a signaling diagram of a process 200 for exchanging
messages for joining a CCG between a non-member AP and a master AP
in accordance with the present invention. A non-member AP, (such as
AP 102d), desiring to join an existing CCG 108 sends a CCG addition
request message to the master AP 102a along with capability
information of the AP 102d and/or BSS information (step 202). The
CCG addition request message includes the CCGI of the requested CCG
108.
The capability information includes, but is not limited to, the
list of frequency channels on which the AP 102d is capable of
camping and information as to whether the AP 102d is capable of
reporting channel utilization or interference measurement. The BSS
information is information related to the BSS served by the AP
102d, (e.g., whether or not the AP 102d is using the common channel
to serve its own BSS, and, if yes, how many STAs are currently
served by the AP 102d).
The master AP 102a determines whether the non-member AP 102d should
be accepted or not and responds to the non-member AP 102d with a
CCG addition response message, which indicates a positive or
negative response (step 204). If the non-member AP 102d receives a
positive response, the AP 102d becomes a part of the CCG 108 and
starts broadcasting the CCGI.
The criteria in determining whether the non-member AP 102d should
be accepted in the CCG 108 include, but are not limited to,
insufficient capabilities, (e.g., not being able to receive on
certain channels), and the number of APs included in the CCG 108,
(since if too many APs are included in the CCG 108, it may result
in poor performance or unacceptable delays in changing the WDS
channel of the CCG 108), or any other relevant factors. The master
AP 102a may measure some factors by itself and those factors need
not be directly communicated by the non-member AP 102d. For
example, the master AP 102a may measure channel loading,
interference, path loss between the non-member AP 102d and the
master AP 102a or received signal strength from the non-member AP
102d, or the like.
The CCG addition request message may be included in any
conventional frame, (e.g., a probe request message or an
association request message), or may be included in a new
stand-alone (management) frame. The CCG addition response message
may also be included in any conventional frame, (e.g., a probe
response frame or an association response frame), or may be
included in a new stand-alone (management) frame.
FIG. 3 is a signaling diagram of a process 300 for exchanging
messages for leaving a CCG between an AP and a master AP in
accordance with the present invention. A member AP, (such as AP
102b), desiring to leave the CCG 108 sends a CCG deletion
notification message to the master AP 102a (step 302). Upon receipt
of the CCG deletion notification message, the AP 102b no longer
belongs to the CCG 108. The CCG deletion notification message may
be included in any conventional frame, (e.g., a disassociation
message), or may be included in a new stand-alone (management)
frame.
The member APs 102b, 102c of the CCG 108 preferably report
measurements to the master AP 102a of the CCG 108. The measurements
to be reported include not only measurements performed by the APs
102b, 102c, but also any measurements reported by STAs 104b, 104c
served by their own BSSs 106b, 106c if the WDS channel is same to
the BSS channel used within their own BSS 106b, 106c. Relevant
measurements that may be reported by each member AP 102b, 102c in
support of channel management within the CCG 108 include, but are
not limited to, interference levels measured on each channel,
channel utilization of each channel, the number of STAs detected on
each channel, and addresses or identifiers of STAs 104b, 104c
currently associated with the APs 102b, 102c. If the BSS channel of
the AP 102b, 102c is same as the WDS channel, a member AP 102b,
102c may notify the master AP 102a of any relevant configuration
modification, (such as the association or disassociation of a STA
104b, 104c served by the AP 102b, 102c).
FIG. 4 is a signaling diagram of a process 400 for exchanging
messages for change of the WDS channel between a member AP 102b,
102c and a master AP 102a in accordance with the present invention.
A member AP 102b, 102c experiencing severe interference conditions
on the currently selected WDS channel may send a channel change
request message to the master AP 102a for a change of the WDS
channel (step 402). The channel change request message may include
an order of preference for a new channel, as well as any
measurement information relevant for selecting a new WDS
channel.
Upon receipt of the channel change request message, the master AP
102a may optionally respond the requesting AP 102b, 102c with a
channel change response message indicating an accept or a reject of
the request (step 404). The master AP 102a then determines whether
a change of the WDS channel is necessary (step 406). Alternatively,
the channel change may be initiated by the master AP 102a without
receiving the channel change request message. If the master AP 102a
determines that the change of the WDS channel is necessary, the
master AP 102a sends all member APs 102b, 102c of the CCG 108 a
channel change command to change the WDS channel to a new channel
(step 412).
The channel change command includes timing information on which the
channel change is executed. With respect to the timing of the
channel change, for those member APs that use the same channel for
the WDS traffic and BSS traffic on their BSSs, the master AP 102a
may consider additional time so that these APs notify the STAs of
their BSSs of the channel change. The master AP 102a may determine
the additional time based on the number of STAs associated with
these APs.
Alternatively, the master AP 102a may send, (i.e., broadcast,
multicast or unicast), a channel change prepare request message to
all member APs 102b, 102c to inform the member APs 102b, 102c of
the new WDS channel to which the master AP 102a intends to switch
(step 408). Each member AP 102b, 102c then responds with a channel
change prepare response message indicating the delay necessary for
them to notify their STAs 104b, 104c of the channel change (step
410). Based on the responses from the member APs 102b, 102c, the
master AP 102a determines the time at which the channel change will
take place, (presumably using the highest delay reported by one of
the member APs 102b, 102c), and signals this time with the channel
change command at step 410.
An AP may create a new CCG. The AP that wants to create a new CCG
selects a CCGI that is not used by any other CCG of the WDS. The AP
first scans all frequency channels on which it is capable of
receiving to detect all CCGIs in use in the WDS. To reduce the
probability that the same CCGI is accidentally reused, the CCGI may
be randomly selected within a predetermined range. After selection
of the CCGI of the new CCG, the AP becomes the master of the newly
created CCG and starts broadcasting the CCGI with the master
indicator set.
Where two or more CCGs are setup, an AP may select a CCG to join an
available CCGs. The selection of a CCG to which an AP attempts to
join may be performed autonomously by an AP, or may be manually
configured through an operation and maintenance (OAM). The manual
selection would be desirable in case there is a small number of APs
in the WDS and it is expected that based on traffic requirements
and AP capabilities the best performance is achieved when the APs
camp on the same WDS channel.
In selecting the CCG, an AP considers capabilities of the different
APs. Certain APs may or may not have the capability of transmitting
packets to other APs of the WDS on a channel other than the one on
which they are camping. In order to maintain connectivity with
other APs of the WDS, an AP not having with this capability should
never create a new CCG unless it is the only AP that is active in
the environment.
The master AP 102a may be manually or autonomously selected and
reselected. If the master AP 102a is selected manually through OAM,
the APs 102b, 102c not selected as a master AP 102a are precluded
from creating a new CCG (in which case they would automatically
become a master AP of the newly created CCG). In manual
configuration, a centrally located AP may be selected as the master
AP to ensure good connectivity with other APs.
By default, the AP that created the CCG becomes the master AP. A
master AP reselection procedure may be triggered autonomously. For
example, the master AP reselection procedure is triggered when the
master AP is down, when the master AP desires leave the CCG, when
the master AP has not transmitted anything for a predetermined
period, when the master AP unsets its master indicator indicating
that the master AP relinquishes mastership, or the like.
In addition, any member AP 102, 102c may trigger the master AP
reselection procedure. FIG. 5 is a signaling diagram of a process
500 for exchanging messages for reselecting a new master AP between
a member AP 102b, 102c and a current master AP 102a in accordance
with the present invention. A member AP 102b, 102c sends a master
AP reselection request message to the master AP 102a (step 502).
Upon reception of the message, the master AP 102a may optionally
send a master AP reselection response message to the requesting AP
102b, 102c (step 504). The master AP 102a then unsets its master
indicator to indicate all other member APs 102b, 102c that a master
AP reselection procedure is triggered (step 506). A master AP
reselection is then performed by the member APs 102b, 102c and the
master AP 102a (step 508).
A new master AP may be selected by any appropriate means. For
example, the new master AP may be selected by exchanging metrics
associated with each of the APs in the CCG. For example, the
metrics may be traffic volume or simply random numbers. The AP with
the highest metric may be selected as a new master AP.
A signaling between the APs and the master AP may be realized as
part of non-IEEE 802.11 protocol. For example, a generic network
management protocol, such as simple network management protocol
(SNMP) or extended markup language (XML) may be used to control,
report and update operational parameters and settings affecting an
AP's choice of the WDS channel and CCG. The parameters and settings
are stored in an AP database such as a management information base
(MIB). Each AP may contain a software, hardware or combined routine
that on a regular or triggered basis checks for updates of the
parameters and settings contained in the AP's database and adjusts
the behavior of the APs accordingly. Alternatively, the software,
hardware or combined routine in the AP on a regular or triggered
basis checks for updates of the parameters and settings in a remote
database relevant for a group of APs or all APs.
An L2 Ethertype or L3 control protocol may also be used to
communicate signaling, bit fields and/or information elements. An
AP may contain a software, hardware or combined communication
routine that interfaces between the external L2 Ethertype or L3
control protocol carried over the IEEE 802.11-based WDS or BSS.
This adjusts operational settings of the AP directly after
receiving such a L2 Ethertype or L3 control protocol message.
Alternatively, it may indirectly adjust by means of one or more
intermediary databases applicable to a single AP or a group of
APs.
Although the features and elements of the present invention are
described in the preferred embodiments in particular combinations,
each feature or element can be used alone without the other
features and elements of the preferred embodiments or in various
combinations with or without other features and elements of the
present invention.
* * * * *
References